This invention relates to a method of forming and bonding fluff pads for diapers and the like, and more particularly, to a method employing an annular drum which achieves both pad formation and thermal bonding on one vacuum drum.
Fluff forming drums have been known for a considerable time--see, for example, co-owned U.S. Pat. No. 3,599,293. Further, both the processes of pad formation and thermal bonding are existing art, yet no one has performed both on a single drum.
A significant product advantage accrues from the invention which performs both of these processes on a single drum--as compared to the separate processes. This advantage resides in retaining the shape of the pad. Diaper producers have expended much effort in developing pad shapes to achieve optimum performance in the take-up of excreta. Yet, the very step of removing the pad from the forming drum distorts the shape. Thus, the bonding step introduces more distortions into the now-unconfirmed pad.
A significant operational advantage resides in the better control of air flows (both forming and bonding) because these can be segmented on the drum. More particularly, these advantages (and others) can be tabulated as follows:
1. Removal of the pad--because of the increased bonding possible with the synthetic fluff mixture, the pads may be removed from the forming molds more cleanly.
2. Integrity of the pad--because the pads are bonded in the forming mold, the initial formation has not been disturbed by handling. This provides the largest amount of fiber entanglement possible and, hence, the greatest bonded fiber areas. It will be appreciated that handling such as bending or extension/compression of the pad tends to dislodge the fiber bonds established in the forming process.
3. Simplicity of mechanism--one drum may be used for both processes thereby eliminating intermediate transfer mechanisms.
4. Cost savings--with the inventive method it is possible to eliminate the tissue overwrap usually present to assist in transporting the pad to the point of insertion into the final product, i.e., disposable diaper, sanitary pad, etc.
The basic process includes first converting wood pulp or other fibrous materials and the bonding polyolefin into fibers suspended in air via a hammermill or other fiberizer. These suspended fibers, called fluff blend, are then collected on a screen surface which allows the air to pass through while retaining the fluff blend.
The screen consists of woven or other formaminous material which has a significantly open area (to air flow) and is formed in the shape of the desired pad. These screen areas or pocket means are supported on a rotating drum through which the air is exhausted.
Pad formation may take place in several steps consisting of fluff blend deposits, additive deposits such as super-absorbents, and scarfing. Scarfing refers to the process of brushing the outside surface of the newly formed pad with a rotating brush roll or similar aggressive surface. These steps may be repeated to form multiple layers of materials in the pad.
The formed pads then continue rotating on the drum into an area where hot air is directed through the pads and exhausted from the drum interior. At least a portion of the pad contains synthetic fibers, i.e., the polyolefin fibers of a melting point lower than the natural (wood) fibers which constitute the majority of the pad. By heating the pad to the melting point of the synthetic fibers but below the wood fibers, the synthetic fibers can be made to melt and "wick" to the wood fibers. Once heated to the bonding temperature, the pads are cooled causing the molten materials to solidify and bond the fiber structure together to achieve the advantages outlined above. The concurrent forming and bonding on a forming drum to provide an undistorted diaper pad is not taught by the prior art, viz., U.S. Pat. Nos. 2,544,019; 2,714,081; 3,201,499; 3,051,369; 3,619,322; 3,939,240; 4,592,708 and 4,666,647.
Other advantages and objects of the invention may be seen in the details of the ensuing specification.